In communication between a radio-tag reader and a radio tag (radio frequency identification (RFID)), it is an important technique to detect that the radio tag enters into an area where the radio-tag reader can perform communication (hereinafter, “communication area”) in saving power and reducing unnecessary radio wave discharge of the radio-tag reader. As a conventional technology for detecting the entrance of the radio tag is disclosed an incoming and outgoing product registration processing system that manages incoming and outgoing of a plurality of products loaded on a delivery carrier using radio tags. The incoming and outgoing product registration processing system includes a gate (corresponding to the radio-tag reader) with a blocking unit on a passage of the delivery carrier. When an item attached with a radio tag and the delivery carrier do not satisfy a predetermined condition, the blocking unit is closed, and the result and cause thereof are reported to a deliverer. In the incoming and outgoing product registration processing system, a sensor of the gate optically detects the passage of the delivery carrier through the gate, and, as a result, when the delivery carrier passes through the gate, a process using the radio tag is performed (for example, see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-open No. 2003-327331